- This story is regularly updated for relevance. Last updated: May 13, 2021
There are a total of five coronavirus vaccines currently in distribution or development for U.S. citizens. All five vaccines provide effective protection from severe disease and death, but they have different degrees of overall efficacy against the virus. There are also varying wait times between those vaccines that require a first and second dose. Here’s what you need to know about how long you’ll likely need to wait between COVID-19 vaccine doses.
Pfizer and Moderna
The Pfizer and Moderna COVID-19 vaccines are very similar to one another. Both vaccines use messenger RNA (also known as mRNA) technology that delivers genetic code and replicates the virus’ surface protein spike. The immune system learns to identify these spike proteins as foreign and then develops antibodies to combat infections.
The recommended interval for the Pfizer-BioNTech vaccine, which is 95% effective, is 21 days between the first and second dose. In contrast, the Moderna vaccine—which is 94.1% effective—recommends 28 days between the first and second dose.
In the event vaccine shortages cause delays to these intervals, the Centers for Disease Control and Prevention says it’s safe to administer the second dose up to six weeks, or 42 days, after the first dose. In some cases, the interval can be even longer with no need to restart the series.
And one leading expert, Michael Osterholm of the Center for Infectious Disease Research and Policy, said he was delaying his second dose indefinitely to make sure the vaccine is available to more people.
Dr. Anthony Fauci, though, said to make sure you actually get that second dose of the vaccine to make sure you’re protected from the COVID variants (study after study have shown that Pfizer performs well against those variants). Still, there seems to be confusion from a percentage of the population who aren’t sure the second dose is necessary.
BioNTech Chief Executive Ugur Sahin, who helped come up with the Pfizer vaccine, advised against extending doses more than six weeks. “As a scientist, I wouldn’t mind if the second dose of the vaccine is given three weeks, four weeks, maybe five weeks, even up to six weeks might still be OK,” he told Sky News. “But I wouldn’t delay that further. As a scientist, I believe that it is not good to go longer than six weeks.”
Researchers at Oxford University found that the AstraZeneca COVID-19 vaccine was 76% effective at preventing symptomatic infection for three months after a single dose. Interestingly, efficacy rates actually rose with longer intervals between doses. In late March, though, U.S. officials said AstraZeneca had used outdated data for some of its results.
When the second dose is administered a minimum of 12 weeks following the first dose, efficacy climbs to 82.4%. If the second dose is administered in six weeks or less, however, the efficacy rate drops to 54.9%. Those who receive the AstraZeneca vaccine can therefore expect to wait at least 12 weeks between doses.
Johnson & Johnson
Johnson & Johnson’s COVID-19 vaccine is comparatively unique. It requires only one dose for 66% protection against moderate to severe infection and is 85% effective against severe disease. The clinical trial reported no instances of hospitalization or death along those who received the vaccine. It was approved for emergency use in the U.S. in late February.
The COVID-19 vaccine in development by Novavax offers more than 89% efficacy against the virus, with two doses required approximately one month apart. The vaccine also requires only basic refrigeration, unlike Pfizer and Moderna’s vaccines, which should help promote widespread distribution.
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